High speed data transmission is becoming increasingly important in the mobile communications industry. Mobile Internet access and IPTV are just two applications that are driving this requirement. Wideband Code Division Multiple Access (WCDMA) uses high-speed downlink (DL) packet access and an enhanced uplink (EUL) to achieve high speed data transfer. Future mobile communication networks may use Interference Cancellation (IC) and Interference Suppression (IS) in order to achieve better performance in terms of, for example, peak data rates, system throughput and system capacity. IC and IS are applicable both on the DL and the uplink (UL).
IS relies on combining received signals such that any interference is suppressed and the Signal to Interference plus Noise Ratio (SINR) is maximized. There are many ways to achieve IS. Examples of IS include interference rejection combining, in which signals from more than one antenna are combined in order to suppress interference, and G-Rake+, in which interference is suppressed by “whitening” of the interference both in the temporal and the spatial domain.
Without IC, the load at the antenna connector can be expressed as the noise rise, or rise over thermal, RoT(t), defined by
                              RoT          ⁡                      (            t            )                          =                              RTWP            ⁡                          (              t              )                                            N            ⁡                          (              t              )                                                          (        1        )            where N(t) is the thermal noise level measured at the antenna connector, and RTWP(t) is defined in Equation 2. This relative measure is not affected by the application of any de-spreading. RTWP(t) is the Received Total Wideband Power and is measured at the antenna connector.
                              RTWP          ⁡                      (            t            )                          =                                            ∑                              k                =                1                            K                        ⁢                                          P                k                            ⁡                              (                t                )                                              +                                    I              N                        ⁡                          (              t              )                                +                      N            ⁡                          (              t              )                                                          (        2        )            
IN(t) denotes the power received from neighbour cells (N) in the WCDMA network. One of the difficulties in estimating RoT is separating the thermal noise power from the interference from neighbour cells.
Another specific problem that needs to be addressed is that the signal reference points are, by definition, at the antenna connector. However, the measurements are obtained after the analogue signal conditioning chain, in the digital receiver. The analogue signal conditioning chain introduces a scale factor error of about 1 dB (1-sigma) that is difficult to compensate for. Fortunately, all powers of Equation 2 are equally affected by the scale factor error so when (1) is calculated, the scale factor error is cancelled as shown in Equation 3:
                                                                                          RoT                  DigitalReceiver                                ⁡                                  (                  t                  )                                            =                            ⁢                                                                    RTWP                    DigitalReceiver                                    ⁡                                      (                    t                    )                                                                                        N                    DigitalReceiver                                    ⁡                                      (                    t                    )                                                                                                                          =                            ⁢                                                                    γ                    ⁡                                          (                      t                      )                                                        ⁢                                                            RTWP                      Antenna                                        ⁡                                          (                      t                      )                                                                                                            γ                    ⁡                                          (                      t                      )                                                        ⁢                                                            N                      Antenna                                        ⁡                                          (                      t                      )                                                                                                                                              =                            ⁢                                                RoT                  Antenna                                ⁡                                  (                  t                  )                                                                                        (        3        )            
γ is a scale factor from the antenna owing to effects of cabling and front end electronics.
In order to understand the fundamental problem of neighbour cell interference when performing load estimation, note thatIN(t)+N(t)=E[IN(t)]+E[N(t)]+ΔIN(t)+ΔN(t)   (4)where E[.] denotes mathematical expectation and where Δ denotes the variation around the mean. Since there are no measurements available in the Radio Base Station (RBS) that are related to the neighbor cell interference, a linear filtering operation can at best estimate the sum E[IN(t)]+E[N(t)]. However, this estimate cannot be used to deduce the value of E[N(t)]. This is because we can only estimate the sum, and not an individual component of the sum. It has been shown that the noise power floor is not mathematically observable.
There are several known ways of estimating RoT. One example is to use a sliding window algorithm, as illustrated in FIG. 1. This algorithm estimates the RoT, as given by Equation 1. The main problem solved by the estimation algorithm is the accurate estimation of the thermal noise floor N(t). Since it is not possible to obtain accurate estimates of N(t) owing to the neighbor cell interference, the estimate therefore uses an approximation, by considering a soft minimum as computed over a relatively long period of time. This estimate of RoT therefore relies on the noise floor being substantially constant over long periods of time, disregarding small temperature drifts
The sliding window algorithm described above has a disadvantage of requiring a large amount of storage memory. This becomes particularly troublesome in scenarios in which a large number of instances of the algorithm are required, for example when IC is introduced in the uplink. To reduce the memory consumption, it is known to use a recursive algorithm that reduces the memory requirements of the sliding window algorithm by a factor of at least 100.
Turning now to cell stability load estimation, this functionality exploits load factors for each user. In their simplest form, the load factors are given by Equation 5, in which:
                                          L            u                    =                                                    P                u                            RTWP                        =                                                            (                                      C                    /                    I                                    )                                u                                            1                +                                                      (                                          C                      /                      I                                        )                                    u                                                                    ,                                  ⁢                  u          =          1                ,        …        ⁢                                  ,        U                            (        5        )            
Lu is the load and Pu is the power of user u. (C/I)u is the carrier to interference ratio of user u. Load factors are then summed for each power-controlled user. In this way, the neighbour cell interference is not included in the resulting load measure. This is a reasonable assumption since the neighbour cell interference should not affect the user's cell power control loop, at least not when first order effects are considered.
Turning now to IC, the conventional procedure to perform IC is summarized by the following steps:    1. The channel of the interferer to be cancelled is estimated;    2. The transmitted signal of the interferer to be cancelled is decoded;    3. A replica of the received signal of the interferer to be cancelled is created by use of the channel and the decoded signal. This replica may be reconstructed as an IQ chip stream; and    4. The replica of the interfering signal is subtracted from the received signal of the user to be decoded, thereby reducing the remaining power of the interferer to very low power levels.
It is important to note that the effect of this procedure is different for different users, since a user causing interference is also a user, and the interference will affect different users in different ways. A consequence for load estimation is that there is not a uniform way to analyse the interference of the WCDMA uplink; the load is individual for each user. As a consequence, combining user interference to an uplink cell load is no longer a trivial matter and requires special measures described below.
Also note that IC with regeneration and subtraction is more straightforward than with G-Rake+ (discussed below) as there is no change of the scale factor for the thermal noise power floor. A consequence is that the RoT estimation algorithms available without IC are still applicable in this case, since a constant noise power level is estimated.
A difference between G-Rake+ and conventional RAKE is that each user perceives a reduced level of interference immediately after a weight combining step. In G-Rake+, a covariance matrix {circumflex over (R)}u, u=1, . . ., U, with the order equal to the number of fingers is estimated to analyse the interference. Any codes not used by a present user u can be used in order to estimate {circumflex over (R)}u.
A G-Rake+ receiver uses an estimated covariance matrix that models the interference in order to compute the combining weights for the users u, u=1, . . ., U.{circumflex over (R)}uŵu=ĥu, u=1, . . . , U   (6)
where ĥu, u=1, . . ., U, is the net channel response of user u and where ŵu are the combining weights.
The effect of Equation (6) is that G-Rake+ essentially ‘whitens’ the correlated interference and removes large spectral peaks from interferers at certain finger locations and for certain antenna elements.
Note that G-Rake+ is a linear receiver. There is a related type of IC receiver for WCDMA which is also linear, denoted the ‘chip equalizer’. The difference between G-Rake+ and the chip equalizer is simply the order of certain basic operations. The following description refers to G-Rake+, but can also be applied to chip equalizers.
In order to estimate load, taking account of the G-Rake+ IC gain, the powers after weight combining are studied. First, it is assumed that the received signal of user u on code k∈Ωu isyu,k=husu,k+Iu,k+Nu,k, u=1, . . . , U, k=1, . . . , K   (7)
where Ωu denotes the set of codes for user u, su,k, u=1, . . ., U, k=1, . . ., K, is the signal, Iu,k, u=1, . . ., U, k=1, . . ., K, is the interference and Nu,k, u=1, . . ., U, k=1, . . ., K, is the (thermal) noise signal (not power) and ĥu, u=1, . . ., U, is the net channel response of user u. G-Rake+ then performs weight combining to obtain statistics zu,kG+ according to the equations{circumflex over (z)}u,kG+=ŵuHyu,k=ŵuHĥusu,k+ŵuHIu,k+ŵuHNu,k, u=1, . . . , U, k=1, . . . , K.   (8){circumflex over (R)}uŵu=ĥu, u=1, . . . , U   (9)
where ŵu are the combining weights of G-Rake+, and {circumflex over (R)}u is the estimated covariance matrix that models the interference for computation of the combining weights for the users. Equations (8) and (9) have two main implications; one indicating how power measurements can be obtained and one indicating the scale factor problem which is addressed below.
Using Equation (8) it can be seen that the effect of the G-Rake+ weight combining is the same as if an artificially generated received signal zu,kG+ had been processed. Since these signals reflect the weight combining and thereby the IC gains of the G-Rake+ receiver, zu,kG+, u=1, . . ., U, k=1, . . ., K is believed to be a relevant starting point for load estimation.
As stated above, the load estimator operates by processing of the RTWP and possibly the RSEPS. For this reason, similar power signals need to be formed from zu,kG+, u=1, . . ., U, k=1, . . ., K, in order to reuse the load concept applied without IC.
In order to estimate user powers associated with the G-Rake+ sufficient statistics, Equation (8) and a low degree of correlation between its three terms is assumed. This leads to:|{circumflex over (z)}u,kG+|2≈ŵuHĥuĥuHŵu|su,k|2+ŵuHIu,kIu,kHŵu+ŵuHNu,kNu,kHŵu≡Su,kG++Iu,kG++Nu,kG+, u=1, . . . , U, k=1, . . . , K   (10)
The RoT, as seen by user u, can now be defined using Equations (11) to (14):
                              RoT          u                      G            +                          ≡                                            S              u                              G                +                                      +                          I              u                              G                +                                      +                          N              u                              G                +                                                          N            u                          G              +                                                          (        11        )                                          S          u                      G            +                          =                              ∑                          k              ∈                              Ω                u                                                                                    ⁢                      S                          u              ,              k                                      G              +                                                          (        12        )                                          I          u                      G            +                          =                              ∑            k                                                          ⁢                      I                          u              ,              k                                      G              +                                                          (        13        )                                          N          u                      G            +                          =                              ∑            k                                                          ⁢                      N                          u              ,              k                                      G              +                                                          (        14        )            
Note that it is difficult to distinguish between Su,kG+, Iu,kG+ and Nu,kG+ for k∈Ωu unless both Iu,kG+ and Nu,kG+ are computed using other quantities. Equation (10) expresses the power using the (transmitted) code power |su,k|2. The same quantity Su,kG+ can also be expressed starting with the antenna power |eu,k|2=ĥuHĥu|su,k|2, in which case Su,kG+=ŵuHŵu|eu,k|2. This latter setting may be used for validation of the concept, but the following discussion uses the definitions provided by Equations (10) to (14).
The signal power SuG+ is computed directly from Equation (12). Combining Equations (10) and (12) results in Equation (15):
                                                                                          S                  u                                      G                    +                                                  =                                ⁢                                                      ∑                                          k                      ∈                                              Ω                        u                                                                                                                                            ⁢                                      S                                          u                      ,                      k                                                              G                      +                                                                                                                                              =                                ⁢                                                                            w                      ^                                        u                    H                                    ⁢                                                            h                      ^                                        u                                    ⁢                                                            h                      ^                                        u                    H                                    ⁢                                                            w                      ^                                        u                                    ⁢                                                            ∑                                              k                        ∈                                                  Ω                          u                                                                                                                                                          ⁢                                                                                                                    s                                                      u                            ,                            k                                                                                                                      2                                                                                                                                              =                                ⁢                                                                            w                      ^                                        u                    H                                    ⁢                                                            h                      ^                                        u                                    ⁢                                                            h                      ^                                        u                    H                                    ⁢                                                            w                      ^                                        u                                    ⁢                                                            E                      ^                                                              s                      ,                      u                                                                                                                                                                =                                    ⁢                                                                                                                                                                                                w                              ^                                                        u                            H                                                    ⁢                                                                                    h                              ^                                                        u                                                                                                                      2                                        ⁢                                                                  E                        ^                                                                    s                        ,                        u                                                                                            ,                                                    ⁢                                  ⁢                              u            =            1                    ,          …          ⁢                                          ,          U                                    (        15        )            
In order to compute the white noise power floor NuG+, the thermal noise power floor estimation algorithm is used to estimate the thermal noise power floor before any G-Rake+ processing. A problem then arises since the thermal noise is scaled by ŵu, and so the thermal noise power level will no longer appear to be constant.
In order to circumvent this problem, a calculation is made of the scale factor by which the thermal noise power is scaled. To compute this quantity, first note that when the wideband thermal noise power floor is estimated before G-Rake+ processing, e.g. with a basic noise floor estimator, the following quantity is estimated
                                                                        N                ^                            =                            ⁢                                                                    1                    M                                    ⁢                                                            ∑                                              m                        =                        1                                            M                                        ⁢                                                                  ∑                                                  k                          =                          1                                                K                                            ⁢                                                                                                    (                                                          N                                                              u                                ,                                k                                                            m                                                        )                                                    H                                                ⁢                                                  N                                                      u                            ,                            k                                                    m                                                                                                                    ⁢                                  →                                      M                    →                    ∞                                                  ⁢                                  KE                  ⁡                                      [                                                                                            (                                                      N                                                          u                              ,                              k                                                                                )                                                H                                            ⁢                                              N                                                  u                          ,                          k                                                                                      ]                                                                                                                          =                            ⁢                              KP                                  N                                      u                    ,                    k                                                                                                                          =                            ⁢                              K                ⁢                                  1                  K                                ⁢                                  P                  N                                                                                                        =                            ⁢                              N                0                                                                        (        16        )            where N0 is the thermal noise power floor and where m is a sample summation index. The power at the sufficient statistics signal processing point is however
                                                                                          N                  ^                                                  G                  +                                            =                            ⁢                                                1                  M                                ⁢                                                      ∑                                          m                      =                      1                                        M                                    ⁢                                                            ∑                                              k                        =                        1                                            K                                        ⁢                                                                                            (                                                                                                                    w                                ^                                                            u                              H                                                        ⁢                                                          N                                                              u                                ,                                k                                                            m                                                                                )                                                H                                            ⁢                                                                        w                          ^                                                u                        H                                            ⁢                                              N                                                  u                          ,                          k                                                m                                                                                                                                                                    =                            ⁢                                                1                  M                                ⁢                                                      ∑                                          m                      =                      1                                        M                                    ⁢                                                            ∑                                              k                        =                        1                                            K                                        ⁢                                          tr                      ⁡                                              (                                                                                                            (                                                                                                                                    w                                    ^                                                                    u                                  H                                                                ⁢                                                                  N                                                                      u                                    ,                                    k                                                                    m                                                                                            )                                                        H                                                    ⁢                                                                                    w                              ^                                                        u                            H                                                    ⁢                                                      N                                                          u                              ,                              k                                                        m                                                                          )                                                                                                                                                                    =                            ⁢                                                1                  M                                ⁢                                                      ∑                                          m                      =                      1                                        M                                    ⁢                                                            ∑                                              k                        =                        1                                            K                                        ⁢                                          tr                      ⁡                                              (                                                                                                            w                              ^                                                        u                            H                                                    ⁢                                                                                                                    N                                                                  u                                  ,                                  k                                                                m                                                            ⁡                                                              (                                                                                                                                            w                                      ^                                                                        u                                    H                                                                    ⁢                                                                      N                                                                          u                                      ,                                      k                                                                        m                                                                                                  )                                                                                      H                                                                          )                                                                                                                                                                    =                            ⁢                                                1                  M                                ⁢                                                      ∑                                          m                      =                      1                                        M                                    ⁢                                                            ∑                                              k                        =                        1                                            K                                        ⁢                                          tr                      ⁡                                              (                                                                                                            w                              ^                                                        u                            H                                                    ⁢                                                                                                                    N                                                                  u                                  ,                                  k                                                                m                                                            ⁡                                                              (                                                                  N                                                                      u                                    ,                                    k                                                                    m                                                                )                                                                                      H                                                    ⁢                                                                                    w                              ^                                                        u                                                                          )                                                                                                                                                                    =                            ⁢                                                tr                  ⁡                                      (                                                                  ∑                                                  k                          =                          1                                                K                                            ⁢                                                                                                                                  w                              ^                                                        u                            H                                                    ⁡                                                      (                                                                                          1                                M                                                            ⁢                                                                                                ∑                                                                      m                                    =                                    1                                                                    M                                                                ⁢                                                                                                                                            N                                                                              u                                        ,                                        k                                                                            m                                                                        ⁡                                                                          (                                                                              N                                                                                  u                                          ,                                          k                                                                                m                                                                            )                                                                                                        H                                                                                                                      )                                                                          ⁢                                                                              w                            ^                                                    u                                                                                      )                                                  ⁢                                  →                                      M                    →                    ∞                                                                                                                                        ⁢                              tr                ⁡                                  (                                      K                    ⁢                                                                  w                        ^                                            u                      H                                        ⁢                                          E                      ⁡                                              [                                                                                                            N                                                              u                                ,                                k                                                                                      ⁡                                                          (                                                              N                                                                  u                                  ,                                  k                                                                                            )                                                                                H                                                ]                                                              ⁢                                                                  w                        ^                                            u                                                        )                                                                                                        =                            ⁢                              tr                ⁡                                  (                                      K                    ⁢                                                                                            w                          ^                                                u                        H                                            ⁡                                              (                                                                              N                            0                                                    /                          K                                                )                                                              ⁢                    I                    ⁢                                                                  w                        ^                                            u                                                        )                                                                                                        =                            ⁢                                                                    w                    ^                                    u                  H                                ⁢                                                      w                    ^                                    u                                ⁢                                  N                  0                                                                                                        =                            ⁢                                                                    w                    ^                                    u                  H                                ⁢                                                      w                    ^                                    u                                ⁢                                                      N                    ^                                    .                                                                                        (        17        )            
The thermal noise floor at the sufficient statistics signal point can therefore be obtained from the noise floor estimate before G-Rake+ processing by a multiplication with the scale factorκuG+=(ŵu)Hŵu, u=1, . . . , U   (18)
This leads to Equation (19):NuG+=κuG−{circumflex over (N)}, u=1, . . . , U   (19)
The computation of the scale factor requires an additional inner product for each user.
The result of Equation (16) may be replaced by a more general assumption given in Equation (20):
                                                                                                              1                    M                                    ⁢                                                            ∑                                              m                        =                        1                                            M                                        ⁢                                                                  ∑                                                  k                          =                          1                                                K                                            ⁢                                                                                                    N                                                          u                              ,                              k                                                        m                                                    ⁡                                                      (                                                          N                                                              u                                ,                                k                                                            m                                                        )                                                                          H                                                                                            ⁢                                  →                                      M                    →                    ∞                                                  ⁢                                  KE                  ⁡                                      [                                                                                            N                                                      u                            ,                            k                                                                          ⁡                                                  (                                                      N                                                          u                              ,                              k                                                                                )                                                                    H                                        ]                                                              =                            ⁢                              K                ⁢                                                      N                    0                                    K                                ⁢                                  R                  N                                                                                                                        =                                ⁢                                                      N                    0                                    ⁢                                      R                    N                                                              ,                                                          (        20        )            
This is used in a scenario in which sampling is fast enough to reflect the shape of the uplink spectrum. In this case it follows that Equation (16) is transformed into Equation (21):
                                                                        N                ^                            =                            ⁢                                                                    1                    M                                    ⁢                                                            ∑                                              m                        =                        1                                            M                                        ⁢                                                                  ∑                                                  k                          =                          1                                                K                                            ⁢                                                                                                    (                                                          N                                                              u                                ,                                k                                                            m                                                        )                                                    H                                                ⁢                                                  N                                                      u                            ,                            k                                                    m                                                                                                                    ⁢                                  →                                      M                    →                    ∞                                                  ⁢                                  KE                  ⁡                                      [                                                                                            (                                                      N                                                          u                              ,                              k                                                                                )                                                H                                            ⁢                                              N                                                  u                          ,                          k                                                                                      ]                                                                                                                          =                            ⁢                              Ktr                ⁡                                  (                                      E                    ⁡                                          [                                                                                                    N                                                          u                              ,                              k                                                                                ⁡                                                      (                                                          N                                                              u                                ,                                k                                                                                      )                                                                          H                                            ]                                                        )                                                                                                        =                            ⁢                                                N                  0                                ⁢                                  tr                  ⁡                                      (                                          R                      N                                        )                                                                                                          (        21        )            
Furthermore, Equation (17) is transformed into Equation (22):{circumflex over (N)}G+=N0tr(ŵuHRnŵu)   (22)
The end result in this case is the scale factor:
                              κ          u                      G            +                          =                              tr            ⁡                          (                                                                    w                    ^                                    u                  H                                ⁢                                  R                  N                                ⁢                                                      w                    ^                                    u                                            )                                            tr            ⁡                          (                              R                N                            )                                                          (        23        )            
IuG+ can be computed using available SINRs. The code power to interference ratio can be expressed according to Equation (24):
                                                        (                              C                /                I                            )                        u                          G              +                                =                                    S              u                              G                +                                                                    I                u                                  G                  +                                            +                              N                u                                  G                  +                                                                    ,                                  ⁢                  u          =          1                ,        …        ⁢                                  ,        U                            (        24        )            
All of the quantities expressed in Equation (24) except for IuG+ have previously been computed, (see Equations (17) to (19)). Using these quantities, Equation (24) can be solved for IuG+ giving:
                                          I            u                          G              +                                =                                                    S                u                                  G                  +                                                                              (                                      C                    /                    I                                    )                                u                                  G                  +                                                      -                                          κ                u                                  G                  +                                            ⁢                              N                ^                                                    ,                                  ⁢                  u          =          1                ,        …        ⁢                                  ,        U                            (        25        )            
The (C/I)uG+ quantity can be directly related to SINR. This is performed as
                                                                                          (                                      C                    /                    I                                    )                                u                                  G                  +                                            =                            ⁢                                                                    (                                                                                                                                                      β                                                              u                                ,                                DPCCH                                                            2                                                        +                                                          β                                                              u                                ,                                EDPCCH                                                            2                                                        +                                                                                                                                                                                                          n                                                              u                                ,                                codes                                                                                      ⁢                                                          β                                                              u                                ,                                EDPDCH                                                            2                                                                                                                                            )                                                                              β                                              u                        ,                        DPCCH                                            2                                        ⁢                                          SF                                              u                        ,                        DPCCH                                                                                            ⁢                                  SINR                  u                                      G                    +                                                                                                                          =                            ⁢                                                                    β                                          u                      ,                      effective                                        2                                                        SF                                          u                      ,                      DPCCH                                                                      ⁢                                  SINR                  u                                      G                    +                                                                                                          (        26        )            
Combining Equations (25) and (26) gives Equation (27):
                              I          u                      G            +                          =                                                            S                u                                  G                  +                                                                              (                                      C                    /                    I                                    )                                u                                  G                  +                                                      -                                          κ                u                                  G                  +                                            ⁢                              N                ^                                              =                                                                      SF                                      u                    ,                    DPCCH                                                                    β                                      u                    ,                    effective                                    2                                            ⁢                                                S                  u                                      G                    +                                                                    SINR                  u                                      G                    +                                                                        -                                          κ                u                                  G                  +                                            ⁢                              N                ^                                                                        (        27        )            
In order to compute RoTuG+, Equations (15), (19) and (27) are inserted into Equation (11), as shown in Equation (28):
                                                                                          RoT                  u                                      G                    +                                                  ≡                                ⁢                                                                            S                      u                                              G                        +                                                              +                                          I                      u                                              G                        +                                                              +                                                                  κ                        u                                                  G                          +                                                                    ⁢                                              N                        ^                                                                                                                        κ                      u                                              G                        +                                                              ⁢                                          N                      ^                                                                                                                                                                =                                    ⁢                                                                                    S                        u                                                  G                          +                                                                                                                      κ                          u                                                      G                            +                                                                          ⁢                                                  N                          ^                                                                                      ⁢                                          (                                              1                        +                                                                                                            SF                                                              u                                ,                                DPCCH                                                                                                                    β                                                              u                                ,                                effective                                                            2                                                                                ⁢                                                      1                                                          SINR                              u                                                              G                                +                                                                                                                                                        )                                                                      ,                                                    ⁢                                  ⁢                              u            =            1                    ,          …          ⁢                                          ,          U                                    (        28        )            
These measures, for each user, can then be combined into an uplink measure as outlined below. Note that it is apparent from Equation (28) that when SINR is high then the RoT for the user is essentially determined by the remaining own power of the user. The RoT then increases when the SINR gets worse.
The computation of the equivalent of RTWP and RSEPS power, at the sufficient statistics signal point, is now described. It follows from Equation (28) that the equivalent of RTWP, seen by user u, becomes:
                                          S                          u              ,              RTWP                                      G              +                                =                                    S              u                              G                +                                      ⁡                          (                              1                +                                                                            SF                                              u                        ,                        DPCCH                                                                                    β                                              u                        ,                        effective                                            2                                                        ⁢                                      1                                          SINR                      u                                              G                        +                                                                                                        )                                      ,                                  ⁢                  u          =          1                ,        …        ⁢                                  ,        U                            (        29        )            
The equivalent of RSEPS, as seen by user u, is therefore obtained by a summation over the RSEPS user codes, when still using ĥu and ŵu 
                                          S                          u              ,              RSEPS                                      G              +                                =                                    ∑                                                u                  RSEPS                                =                1                                            U                RSEPS                                      ⁢                          S                              u                ⁡                                  (                                      u                    RSPES                                    )                                                            G                +                                                    ,                                  ⁢                  u          =          1                ,        …        ⁢                                  ,        U                            (        30        )                                                                                                      S                                      u                    ⁡                                          (                                              u                        RSEPS                                            )                                                                            G                    +                                                  =                                ⁢                                                      ∑                                          k                      ∈                                              Ω                                                  u                          ⁡                                                      (                                                          u                              RSEPS                                                        )                                                                                                                                                                                              ⁢                                      S                                          u                      ,                      k                                                              G                      +                                                                                                                                              =                                ⁢                                                                            w                      ^                                        u                    H                                    ⁢                                                            h                      ^                                        u                                    ⁢                                                            h                      ^                                        u                    H                                    ⁢                                                            w                      ^                                        u                                    ⁢                                                            ∑                                              k                        ∈                                                  Ω                                                      u                            ⁡                                                          (                                                              u                                RSEPS                                                            )                                                                                                                                                                                                                ⁢                                                                                                                    s                                                      u                            ,                            k                                                                                                                      2                                                                                                                                              =                                ⁢                                                                            w                      ^                                        u                    H                                    ⁢                                                            h                      ^                                        u                                    ⁢                                                            h                      ^                                        u                    H                                    ⁢                                                            w                      ^                                        u                                    ⁢                                                            E                      ^                                                              s                      ,                                              u                        ⁡                                                  (                                                      u                            RSPES                                                    )                                                                                                                                                                                                              =                                    ⁢                                                                                                                                                                                                w                              ^                                                        u                            H                                                    ⁢                                                                                    h                              ^                                                        u                                                                                                                      2                                        ⁢                                                                  E                        ^                                                                    s                        ,                                                  u                          ⁡                                                      (                                                          u                              RSEPS                                                        )                                                                                                                                              ,                                                    ⁢                                  ⁢                                            u              RSEPS                        =            1                    ,          …          ⁢                                          ,                      U            RSEPS                                              (        31        )            
Note that the channel model of user u is retained when summing over the codes of the RSEPS users, and so the computation needs to be performed once for each user.
In order to obtain an uplink load measure when using G-Rake+, an average load measure can be obtained. Averaging over all users using Equation (28) gives the uplink load measure:
                              〈                      RoT                          G              +                                〉                =                              1            U                    ⁢                                    ∑                              u                =                1                            U                        ⁢                          RoT              u                              G                +                                                                        (        32        )            
This measure may not be suitable since it does not capture the effect of users with poor IC gain. It is these users that are more likely to cause instability owing to power increases. Similarly, the averaged RTWP and RSEPS measures become:
                              〈                      S            RTWP                          G              +                                〉                =                              1            U                    ⁢                                    ∑                              u                =                1                            U                        ⁢                          S                              u                ,                RTWP                                            G                +                                                                        (        33        )                                          〈                      S            RSEPS                          G              +                                〉                =                              1            U                    ⁢                                    ∑                              u                =                1                            U                        ⁢                                          S                                  u                  ,                  RSEPS                                                  G                  +                                            .                                                          (        34        )            
Rather than performing averaging, an alternative approach is to use a worst case approach, in which the averaging is replaced by a maximum operation. This means that load estimation is performed by estimated the load perceived by the user that perceives the maximum total load. This conservative approach may improve cell stability arguments, although it may be too conservative. The worst case load is defined by Equations (35) to (38):
                              u          max                =                  arg          ⁢                                          ⁢                                    max              u                        ⁢                          (                              RoT                u                                  G                  +                                            )                                                          (        35        )                                          max          ⁡                      (                          RoT              u                              G                +                                      )                          =                  RoT                      u            max                                G            +                                              (        36        )                                          max          ⁡                      (                          S              RTWP                              G                +                                      )                          =                  S                                    u              max                        ,            RTWP                                G            +                                              (        37        )                                          max          ⁡                      (                          S              RSEPS                              G                +                                      )                          =                  S                                    u              max                        ,            RSEPS                                G            +                                              (        38        )            
A third alternative to obtain an uplink load measure when using G-Rake+ is to obtain RoTuG+ for each user, and then select a user corresponding to a predetermined percentile.
The equations above show how an uplink cell load can be computed in terms of the RoT after G-Rake+ or chip equalizer whitening of the interference, as experienced by each user. Note that the interference caused by a user on other users may have a very different effect on the RoT experienced by further users. However, according to prior art disclosures, the RoT experienced by the users of the cell can be combined to a cell load, preferably using the user that experiences the worst RoT conditions.
When advanced receivers that cancel or suppress interference from other users are applied, such as G-Rake+, the conventional load measure without interference suppression is no longer valid. The conventional load measure is based on the assumption that each user affects all other users in exactly the same way, from a load perspective, since conventional receivers do not handle the interference from other users in any explicit way in the receiver. However, with advanced receivers such as G-Rake+, a user's effect on other users is not the same on all users, and the effect is a function of the IC or IS efficiency.
The load of the cell is used for scheduling of uplink EUL users (either existing users or new users joining the RAN). When performing scheduling, the cell load measure described for G-Rake+ provides a total scheduling headroom as compared to pre-determined thresholds. However, known solutions do not address the detailed impact and contribution of different existing users to the uplink RoT after G-Rake+ processing, and so the scheduler can not take this into account.